/* trees.c -- output deflated data using Huffman coding
 * Copyright (C) 1992-1993 Jean-loup Gailly
 * This is free software; you can redistribute it and/or modify it under the
 * terms of the GNU General Public License, see the file COPYING.
 */

#include <ctype.h>
#include "gzip.h"

/* ===========================================================================
 * Constants
 */

#define MAX_BITS 15
/* All codes must not exceed MAX_BITS bits */

#define MAX_BL_BITS 7
/* Bit length codes must not exceed MAX_BL_BITS bits */

#define LENGTH_CODES 29
/* number of length codes, not counting the special END_BLOCK code */

#define LITERALS  256
/* number of literal bytes 0..255 */

#define END_BLOCK 256
/* end of block literal code */

#define L_CODES (LITERALS+1+LENGTH_CODES)
/* number of Literal or Length codes, including the END_BLOCK code */

#define D_CODES   30
/* number of distance codes */

#define BL_CODES  19
/* number of codes used to transfer the bit lengths */


local int extra_lbits[LENGTH_CODES] /* extra bits for each length code */
	= {0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,0};

local int extra_dbits[D_CODES] /* extra bits for each distance code */
	= {0,0,0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13};

local int extra_blbits[BL_CODES]/* extra bits for each bit length code */
	= {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3,7};

#define STORED_BLOCK 0
#define STATIC_TREES 1
#define DYN_TREES    2
/* The three kinds of block type */

#ifndef LIT_BUFSIZE
#  ifdef SMALL_MEM
#    define LIT_BUFSIZE  0x2000
#  else
#  ifdef MEDIUM_MEM
#    define LIT_BUFSIZE  0x4000
#  else
#    define LIT_BUFSIZE  0x8000
#  endif
#  endif
#endif
#ifndef DIST_BUFSIZE
#  define DIST_BUFSIZE  LIT_BUFSIZE
#endif
/* Sizes of match buffers for literals/lengths and distances.  There are
 * 4 reasons for limiting LIT_BUFSIZE to 64K:
 *   - frequencies can be kept in 16 bit counters
 *   - if compression is not successful for the first block, all input data is
 *     still in the window so we can still emit a stored block even when input
 *     comes from standard input.  (This can also be done for all blocks if
 *     LIT_BUFSIZE is not greater than 32K.)
 *   - if compression is not successful for a file smaller than 64K, we can
 *     even emit a stored file instead of a stored block (saving 5 bytes).
 *   - creating new Huffman trees less frequently may not provide fast
 *     adaptation to changes in the input data statistics. (Take for
 *     example a binary file with poorly compressible code followed by
 *     a highly compressible string table.) Smaller buffer sizes give
 *     fast adaptation but have of course the overhead of transmitting trees
 *     more frequently.
 *   - I can't count above 4
 * The current code is general and allows DIST_BUFSIZE < LIT_BUFSIZE (to save
 * memory at the expense of compression). Some optimizations would be possible
 * if we rely on DIST_BUFSIZE == LIT_BUFSIZE.
 */
#if LIT_BUFSIZE > INBUFSIZ
	error cannot overlay l_buf and inbuf
#endif

#define REP_3_6      16
/* repeat previous bit length 3-6 times (2 bits of repeat count) */

#define REPZ_3_10    17
/* repeat a zero length 3-10 times  (3 bits of repeat count) */

#define REPZ_11_138  18
/* repeat a zero length 11-138 times  (7 bits of repeat count) */

/* ===========================================================================
 * Local data
 */

/* Data structure describing a single value and its code string. */
typedef struct ct_data {
	union {
		ush  freq;       /* frequency count */
		ush  code;       /* bit string */
	} fc;
	union {
		ush  dad;        /* father node in Huffman tree */
		ush  len;        /* length of bit string */
	} dl;
} ct_data;

#define Freq fc.freq
#define Code fc.code
#define Dad  dl.dad
#define Len  dl.len

#define HEAP_SIZE (2*L_CODES+1)
/* maximum heap size */

local ct_data dyn_ltree[HEAP_SIZE];   /* literal and length tree */
local ct_data dyn_dtree[2*D_CODES+1]; /* distance tree */

local ct_data static_ltree[L_CODES+2];
/* The static literal tree. Since the bit lengths are imposed, there is no
 * need for the L_CODES extra codes used during heap construction. However
 * The codes 286 and 287 are needed to build a canonical tree (see ct_init
 * below).
 */

local ct_data static_dtree[D_CODES];
/* The static distance tree. (Actually a trivial tree since all codes use
 * 5 bits.)
 */

local ct_data bl_tree[2*BL_CODES+1];
/* Huffman tree for the bit lengths */

typedef struct tree_desc {
	ct_data *dyn_tree;      /* the dynamic tree */
	ct_data *static_tree;   /* corresponding static tree or NULL */
	int     *extra_bits;    /* extra bits for each code or NULL */
	int     extra_base;          /* base index for extra_bits */
	int     elems;               /* max number of elements in the tree */
	int     max_length;          /* max bit length for the codes */
	int     max_code;            /* largest code with non zero frequency */
} tree_desc;

local tree_desc l_desc =
{dyn_ltree, static_ltree, extra_lbits, LITERALS+1, L_CODES, MAX_BITS, 0};

local tree_desc d_desc =
{dyn_dtree, static_dtree, extra_dbits, 0,          D_CODES, MAX_BITS, 0};

local tree_desc bl_desc =
{bl_tree, (ct_data *)0, extra_blbits, 0,      BL_CODES, MAX_BL_BITS, 0};


local ush bl_count[MAX_BITS+1];
/* number of codes at each bit length for an optimal tree */

local uch bl_order[BL_CODES]
	= {16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15};
/* The lengths of the bit length codes are sent in order of decreasing
 * probability, to avoid transmitting the lengths for unused bit length codes.
 */

local int heap[2*L_CODES+1]; /* heap used to build the Huffman trees */
local int heap_len;               /* number of elements in the heap */
local int heap_max;               /* element of largest frequency */
/* The sons of heap[n] are heap[2*n] and heap[2*n+1]. heap[0] is not used.
 * The same heap array is used to build all trees.
 */

local uch depth[2*L_CODES+1];
/* Depth of each subtree used as tie breaker for trees of equal frequency */

local uch length_code[MAX_MATCH-MIN_MATCH+1];
/* length code for each normalized match length (0 == MIN_MATCH) */

local uch dist_code[512];
/* distance codes. The first 256 values correspond to the distances
 * 3 .. 258, the last 256 values correspond to the top 8 bits of
 * the 15 bit distances.
 */

local int base_length[LENGTH_CODES];
/* First normalized length for each code (0 = MIN_MATCH) */

local int base_dist[D_CODES];
/* First normalized distance for each code (0 = distance of 1) */

#define l_buf inbuf
/* DECLARE(uch, l_buf, LIT_BUFSIZE);  buffer for literals or lengths */

/* DECLARE(ush, d_buf, DIST_BUFSIZE); buffer for distances */

local uch flag_buf[(LIT_BUFSIZE/8)];
/* flag_buf is a bit array distinguishing literals from lengths in
 * l_buf, thus indicating the presence or absence of a distance.
 */

local unsigned last_lit;    /* running index in l_buf */
local unsigned last_dist;   /* running index in d_buf */
local unsigned last_flags;  /* running index in flag_buf */
local uch flags;            /* current flags not yet saved in flag_buf */
local uch flag_bit;         /* current bit used in flags */
/* bits are filled in flags starting at bit 0 (least significant).
 * Note: these flags are overkill in the current code since we don't
 * take advantage of DIST_BUFSIZE == LIT_BUFSIZE.
 */

local ulg opt_len;        /* bit length of current block with optimal trees */
local ulg static_len;     /* bit length of current block with static trees */

local ulg compressed_len; /* total bit length of compressed file */

local ulg input_len;      /* total byte length of input file */
/* input_len is for debugging only since we can get it by other means. */

extern long block_start;       /* window offset of current block */
extern unsigned strstart; /* window offset of current string */

/* ===========================================================================
 * Local (static) routines in this file.
 */

local void init_block     OF((void));
local void pqdownheap     OF((ct_data *tree, int k));
local void gen_bitlen     OF((tree_desc *desc));
local void gen_codes      OF((ct_data *tree, int max_code));
local void build_tree     OF((tree_desc *desc));
local void scan_tree      OF((ct_data *tree, int max_code));
local void send_tree      OF((ct_data *tree, int max_code));
local int  build_bl_tree  OF((void));
local void send_all_trees OF((int lcodes, int dcodes, int blcodes));
local void compress_block OF((ct_data *ltree, ct_data *dtree));


#define send_code(c, tree) send_bits(tree[c].Code, tree[c].Len)
/* Send a code of the given tree. c and tree must not have side effects */

#define d_code(dist) \
	((dist) < 256 ? dist_code[dist] : dist_code[256+((dist)>>7)])
/* Mapping from a distance to a distance code. dist is the distance - 1 and
 * must not have side effects. dist_code[256] and dist_code[257] are never
 * used.
 */

#define MAX(a,b) (a >= b ? a : b)
/* the arguments must not have side effects */

/* ===========================================================================
 * Allocate the match buffer, initialize the various tables and save the
 * location of the internal file attribute (ascii/binary) and method
 * (DEFLATE/STORE).
 */
void ct_init(void)
{
	int n;        /* iterates over tree elements */
	int bits;     /* bit counter */
	int length;   /* length value */
	int code;     /* code value */
	int dist;     /* distance index */

	compressed_len = input_len = 0L;

	if (static_dtree[0].Len != 0) return; /* ct_init already called */

	/* Initialize the mapping length (0..255) -> length code (0..28) */
	length = 0;
	for (code = 0; code < LENGTH_CODES-1; code++) {
		base_length[code] = length;
		for (n = 0; n < (1<<extra_lbits[code]); n++) {
			length_code[length++] = (uch)code;
		}
	}
	/* Note that the length 255 (match length 258) can be represented
	 * in two different ways: code 284 + 5 bits or code 285, so we
	 * overwrite length_code[255] to use the best encoding:
	 */
	length_code[length-1] = (uch)code;

	/* Initialize the mapping dist (0..32K) -> dist code (0..29) */
	dist = 0;
	for (code = 0 ; code < 16; code++) {
		base_dist[code] = dist;
		for (n = 0; n < (1<<extra_dbits[code]); n++) {
			dist_code[dist++] = (uch)code;
		}
	}
	dist >>= 7; /* from now on, all distances are divided by 128 */
	for ( ; code < D_CODES; code++) {
		base_dist[code] = dist << 7;
		for (n = 0; n < (1<<(extra_dbits[code]-7)); n++) {
			dist_code[256 + dist++] = (uch)code;
		}
	}

	/* Construct the codes of the static literal tree */
	for (bits = 0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;
	n = 0;
	while (n <= 143) static_ltree[n++].Len = 8, bl_count[8]++;
	while (n <= 255) static_ltree[n++].Len = 9, bl_count[9]++;
	while (n <= 279) static_ltree[n++].Len = 7, bl_count[7]++;
	while (n <= 287) static_ltree[n++].Len = 8, bl_count[8]++;
	/* Codes 286 and 287 do not exist, but we must include them in the
	 * tree construction to get a canonical Huffman tree (longest code
	 * all ones)
	 */
	gen_codes((ct_data *)static_ltree, L_CODES+1);

	/* The static distance tree is trivial: */
	for (n = 0; n < D_CODES; n++) {
		static_dtree[n].Len = 5;
		static_dtree[n].Code = bi_reverse(n, 5);
	}

	/* Initialize the first block of the first file: */
	init_block();
}

/* ===========================================================================
 * Initialize a new block.
 */
local void init_block()
{
	int n; /* iterates over tree elements */

	/* Initialize the trees. */
	for (n = 0; n < L_CODES;  n++) dyn_ltree[n].Freq = 0;
	for (n = 0; n < D_CODES;  n++) dyn_dtree[n].Freq = 0;
	for (n = 0; n < BL_CODES; n++) bl_tree[n].Freq = 0;

	dyn_ltree[END_BLOCK].Freq = 1;
	opt_len = static_len = 0L;
	last_lit = last_dist = last_flags = 0;
	flags = 0; flag_bit = 1;
}

#define SMALLEST 1
/* Index within the heap array of least frequent node in the Huffman tree */


/* ===========================================================================
 * Remove the smallest element from the heap and recreate the heap with
 * one less element. Updates heap and heap_len.
 */
#define pqremove(tree, top) \
{\
	top = heap[SMALLEST]; \
	heap[SMALLEST] = heap[heap_len--]; \
	pqdownheap(tree, SMALLEST); \
}

/* ===========================================================================
 * Compares to subtrees, using the tree depth as tie breaker when
 * the subtrees have equal frequency. This minimizes the worst case length.
 */
#define smaller(tree, n, m) \
	(tree[n].Freq < tree[m].Freq || \
	(tree[n].Freq == tree[m].Freq && depth[n] <= depth[m]))

/* ===========================================================================
 * Restore the heap property by moving down the tree starting at node k,
 * exchanging a node with the smallest of its two sons if necessary, stopping
 * when the heap property is re-established (each father smaller than its
 * two sons).
 */
local void pqdownheap(tree, k)
	ct_data *tree;  /* the tree to restore */
	int k;               /* node to move down */
{
	int v = heap[k];
	int j = k << 1;  /* left son of k */
	while (j <= heap_len) {
		/* Set j to the smallest of the two sons: */
		if (j < heap_len && smaller(tree, heap[j+1], heap[j])) j++;

		/* Exit if v is smaller than both sons */
		if (smaller(tree, v, heap[j])) break;

		/* Exchange v with the smallest son */
		heap[k] = heap[j];  k = j;

		/* And continue down the tree, setting j to the left son of k */
		j <<= 1;
	}
	heap[k] = v;
}

/* ===========================================================================
 * Compute the optimal bit lengths for a tree and update the total bit length
 * for the current block.
 * IN assertion: the fields freq and dad are set, heap[heap_max] and
 *    above are the tree nodes sorted by increasing frequency.
 * OUT assertions: the field len is set to the optimal bit length, the
 *     array bl_count contains the frequencies for each bit length.
 *     The length opt_len is updated; static_len is also updated if stree is
 *     not null.
 */
local void gen_bitlen(desc)
	tree_desc *desc; /* the tree descriptor */
{
	ct_data *tree  = desc->dyn_tree;
	int *extra     = desc->extra_bits;
	int base            = desc->extra_base;
	int max_code        = desc->max_code;
	int max_length      = desc->max_length;
	ct_data *stree = desc->static_tree;
	int h;              /* heap index */
	int n, m;           /* iterate over the tree elements */
	int bits;           /* bit length */
	int xbits;          /* extra bits */
	ush f;              /* frequency */
	int overflow = 0;   /* number of elements with bit length too large */

	for (bits = 0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;

	/* In a first pass, compute the optimal bit lengths (which may
	 * overflow in the case of the bit length tree).
	 */
	tree[heap[heap_max]].Len = 0; /* root of the heap */

	for (h = heap_max+1; h < HEAP_SIZE; h++) {
		n = heap[h];
		bits = tree[tree[n].Dad].Len + 1;
		if (bits > max_length) bits = max_length, overflow++;
		tree[n].Len = (ush)bits;
		/* We overwrite tree[n].Dad which is no longer needed */

		if (n > max_code) continue; /* not a leaf node */

		bl_count[bits]++;
		xbits = 0;
		if (n >= base) xbits = extra[n-base];
		f = tree[n].Freq;
		opt_len += (ulg)f * (bits + xbits);
		if (stree) static_len += (ulg)f * (stree[n].Len + xbits);
	}
	if (overflow == 0) return;

	/* Find the first bit length which could increase: */
	do {
		bits = max_length-1;
		while (bl_count[bits] == 0) bits--;
		bl_count[bits]--;      /* move one leaf down the tree */
		bl_count[bits+1] += 2; /* move one overflow item as its brother */
		bl_count[max_length]--;
		/* The brother of the overflow item also moves one step up,
		 * but this does not affect bl_count[max_length]
		 */
		overflow -= 2;
	} while (overflow > 0);

	/* Now recompute all bit lengths, scanning in increasing frequency.
	 * h is still equal to HEAP_SIZE. (It is simpler to reconstruct all
	 * lengths instead of fixing only the wrong ones. This idea is taken
	 * from 'ar' written by Haruhiko Okumura.)
	 */
	for (bits = max_length; bits != 0; bits--) {
		n = bl_count[bits];
		while (n != 0) {
			m = heap[--h];
			if (m > max_code) continue;
			if (tree[m].Len != (unsigned) bits) {
				opt_len += ((long)bits-(long)tree[m].Len)*(long)tree[m].Freq;
				tree[m].Len = (ush)bits;
			}
			n--;
		}
	}
}

/* ===========================================================================
 * Generate the codes for a given tree and bit counts (which need not be
 * optimal).
 * IN assertion: the array bl_count contains the bit length statistics for
 * the given tree and the field len is set for all tree elements.
 * OUT assertion: the field code is set for all tree elements of non
 *     zero code length.
 */
local void gen_codes (tree, max_code)
	ct_data *tree;        /* the tree to decorate */
	int max_code;              /* largest code with non zero frequency */
{
	ush next_code[MAX_BITS+1]; /* next code value for each bit length */
	ush code = 0;              /* running code value */
	int bits;                  /* bit index */
	int n;                     /* code index */

	/* The distribution counts are first used to generate the code values
	 * without bit reversal.
	 */
	for (bits = 1; bits <= MAX_BITS; bits++) {
		next_code[bits] = code = (code + bl_count[bits-1]) << 1;
	}
	/* Check that the bit counts in bl_count are consistent. The last code
	 * must be all ones.
	 */

	for (n = 0;  n <= max_code; n++) {
		int len = tree[n].Len;
		if (len == 0) continue;
		/* Now reverse the bits */
		tree[n].Code = bi_reverse(next_code[len]++, len);
	}
}

/* ===========================================================================
 * Construct one Huffman tree and assigns the code bit strings and lengths.
 * Update the total bit length for the current block.
 * IN assertion: the field freq is set for all tree elements.
 * OUT assertions: the fields len and code are set to the optimal bit length
 *     and corresponding code. The length opt_len is updated; static_len is
 *     also updated if stree is not null. The field max_code is set.
 */
local void build_tree(desc)
	tree_desc *desc; /* the tree descriptor */
{
	ct_data *tree   = desc->dyn_tree;
	ct_data *stree  = desc->static_tree;
	int elems            = desc->elems;
	int n, m;          /* iterate over heap elements */
	int max_code = -1; /* largest code with non zero frequency */
	int node = elems;  /* next internal node of the tree */

	/* Construct the initial heap, with least frequent element in
	 * heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
	 * heap[0] is not used.
	 */
	heap_len = 0, heap_max = HEAP_SIZE;

	for (n = 0; n < elems; n++) {
		if (tree[n].Freq != 0) {
			heap[++heap_len] = max_code = n;
			depth[n] = 0;
		} else {
			tree[n].Len = 0;
		}
	}

	/* The pkzip format requires that at least one distance code exists,
	 * and that at least one bit should be sent even if there is only one
	 * possible code. So to avoid special checks later on we force at least
	 * two codes of non zero frequency.
	 */
	while (heap_len < 2) {
		int new = heap[++heap_len] = (max_code < 2 ? ++max_code : 0);
		tree[new].Freq = 1;
		depth[new] = 0;
		opt_len--; if (stree) static_len -= stree[new].Len;
		/* new is 0 or 1 so it does not have extra bits */
	}
	desc->max_code = max_code;

	/* The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
	 * establish sub-heaps of increasing lengths:
	 */
	for (n = heap_len/2; n >= 1; n--) pqdownheap(tree, n);

	/* Construct the Huffman tree by repeatedly combining the least two
	 * frequent nodes.
	 */
	do {
		pqremove(tree, n);   /* n = node of least frequency */
		m = heap[SMALLEST];  /* m = node of next least frequency */

		heap[--heap_max] = n; /* keep the nodes sorted by frequency */
		heap[--heap_max] = m;

		/* Create a new node father of n and m */
		tree[node].Freq = tree[n].Freq + tree[m].Freq;
		depth[node] = (uch) (MAX(depth[n], depth[m]) + 1);
		tree[n].Dad = tree[m].Dad = (ush)node;
		/* and insert the new node in the heap */
		heap[SMALLEST] = node++;
		pqdownheap(tree, SMALLEST);

	} while (heap_len >= 2);

	heap[--heap_max] = heap[SMALLEST];

	/* At this point, the fields freq and dad are set. We can now
	 * generate the bit lengths.
	 */
	gen_bitlen((tree_desc *)desc);

	/* The field len is now set, we can generate the bit codes */
	gen_codes ((ct_data *)tree, max_code);
}

/* ===========================================================================
 * Scan a literal or distance tree to determine the frequencies of the codes
 * in the bit length tree. Updates opt_len to take into account the repeat
 * counts. (The contribution of the bit length codes will be added later
 * during the construction of bl_tree.)
 */
local void scan_tree (tree, max_code)
	ct_data *tree; /* the tree to be scanned */
	int max_code;       /* and its largest code of non zero frequency */
{
	int n;                     /* iterates over all tree elements */
	int prevlen = -1;          /* last emitted length */
	int curlen;                /* length of current code */
	int nextlen = tree[0].Len; /* length of next code */
	int count = 0;             /* repeat count of the current code */
	int max_count = 7;         /* max repeat count */
	int min_count = 4;         /* min repeat count */

	if (nextlen == 0) max_count = 138, min_count = 3;
	tree[max_code+1].Len = (ush)0xffff; /* guard */

	for (n = 0; n <= max_code; n++) {
		curlen = nextlen; nextlen = tree[n+1].Len;
		if (++count < max_count && curlen == nextlen) {
			continue;
		} else if (count < min_count) {
			bl_tree[curlen].Freq += count;
		} else if (curlen != 0) {
			if (curlen != prevlen) bl_tree[curlen].Freq++;
			bl_tree[REP_3_6].Freq++;
		} else if (count <= 10) {
			bl_tree[REPZ_3_10].Freq++;
		} else {
			bl_tree[REPZ_11_138].Freq++;
		}
		count = 0; prevlen = curlen;
		if (nextlen == 0) {
			max_count = 138, min_count = 3;
		} else if (curlen == nextlen) {
			max_count = 6, min_count = 3;
		} else {
			max_count = 7, min_count = 4;
		}
	}
}

/* ===========================================================================
 * Send a literal or distance tree in compressed form, using the codes in
 * bl_tree.
 */
local void send_tree (tree, max_code)
	ct_data *tree; /* the tree to be scanned */
	int max_code;       /* and its largest code of non zero frequency */
{
	int n;                     /* iterates over all tree elements */
	int prevlen = -1;          /* last emitted length */
	int curlen;                /* length of current code */
	int nextlen = tree[0].Len; /* length of next code */
	int count = 0;             /* repeat count of the current code */
	int max_count = 7;         /* max repeat count */
	int min_count = 4;         /* min repeat count */

	/* tree[max_code+1].Len = -1; */  /* guard already set */
	if (nextlen == 0) max_count = 138, min_count = 3;

	for (n = 0; n <= max_code; n++) {
		curlen = nextlen; nextlen = tree[n+1].Len;
		if (++count < max_count && curlen == nextlen) {
			continue;
		} else if (count < min_count) {
			do { send_code(curlen, bl_tree); } while (--count != 0);

		} else if (curlen != 0) {
			if (curlen != prevlen) {
				send_code(curlen, bl_tree); count--;
			}
			send_code(REP_3_6, bl_tree); send_bits(count-3, 2);

		} else if (count <= 10) {
			send_code(REPZ_3_10, bl_tree); send_bits(count-3, 3);

		} else {
			send_code(REPZ_11_138, bl_tree); send_bits(count-11, 7);
		}
		count = 0; prevlen = curlen;
		if (nextlen == 0) {
			max_count = 138, min_count = 3;
		} else if (curlen == nextlen) {
			max_count = 6, min_count = 3;
		} else {
			max_count = 7, min_count = 4;
		}
	}
}

/* ===========================================================================
 * Construct the Huffman tree for the bit lengths and return the index in
 * bl_order of the last bit length code to send.
 */
local int build_bl_tree()
{
	int max_blindex;  /* index of last bit length code of non zero freq */

	/* Determine the bit length frequencies for literal and distance trees */
	scan_tree((ct_data *)dyn_ltree, l_desc.max_code);
	scan_tree((ct_data *)dyn_dtree, d_desc.max_code);

	/* Build the bit length tree: */
	build_tree((tree_desc *)(&bl_desc));
	/* opt_len now includes the length of the tree representations, except
	 * the lengths of the bit lengths codes and the 5+5+4 bits for the counts.
	 */

	/* Determine the number of bit length codes to send. The pkzip format
	 * requires that at least 4 bit length codes be sent. (appnote.txt says
	 * 3 but the actual value used is 4.)
	 */
	for (max_blindex = BL_CODES-1; max_blindex >= 3; max_blindex--) {
		if (bl_tree[bl_order[max_blindex]].Len != 0) break;
	}
	/* Update opt_len to include the bit length tree and counts */
	opt_len += 3*(max_blindex+1) + 5+5+4;

	return max_blindex;
}

/* ===========================================================================
 * Send the header for a block using dynamic Huffman trees: the counts, the
 * lengths of the bit length codes, the literal tree and the distance tree.
 * IN assertion: lcodes >= 257, dcodes >= 1, blcodes >= 4.
 */
local void send_all_trees(lcodes, dcodes, blcodes)
	int lcodes, dcodes, blcodes; /* number of codes for each tree */
{
	int rank;                    /* index in bl_order */

	send_bits(lcodes-257, 5); /* not +255 as stated in appnote.txt */
	send_bits(dcodes-1,   5);
	send_bits(blcodes-4,  4); /* not -3 as stated in appnote.txt */
	for (rank = 0; rank < blcodes; rank++) {
		send_bits(bl_tree[bl_order[rank]].Len, 3);
	}

	send_tree((ct_data *)dyn_ltree, lcodes-1); /* send the literal tree */

	send_tree((ct_data *)dyn_dtree, dcodes-1); /* send the distance tree */
}

/* ===========================================================================
 * Determine the best encoding for the current block: dynamic trees, static
 * trees or store, and output the encoded block to the zip file. This function
 * returns the total compressed length for the file so far.
 */
ulg flush_block(buf, stored_len, eof)
	char *buf;        /* input block, or NULL if too old */
	ulg stored_len;   /* length of input block */
	int eof;          /* true if this is the last block for a file */
{
	ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */
	int max_blindex;  /* index of last bit length code of non zero freq */

	flag_buf[last_flags] = flags; /* Save the flags for the last 8 items */

	/* Construct the literal and distance trees */
	build_tree((tree_desc *)(&l_desc));

	build_tree((tree_desc *)(&d_desc));
	/* At this point, opt_len and static_len are the total bit lengths of
	 * the compressed block data, excluding the tree representations.
	 */

	/* Build the bit length tree for the above two trees, and get the index
	 * in bl_order of the last bit length code to send.
	 */
	max_blindex = build_bl_tree();

	/* Determine the best encoding. Compute first the block length in bytes */
	opt_lenb = (opt_len+3+7)>>3;
	static_lenb = (static_len+3+7)>>3;
	input_len += stored_len; /* for debugging only */

	if (static_lenb <= opt_lenb) opt_lenb = static_lenb;

	/* If compression failed and this is the first and last block,
	 * and if the zip file can be seeked (to rewrite the local header),
	 * the whole file is transformed into a stored file:
	 */
	if (stored_len <= opt_lenb && eof && compressed_len == 0L && seekable()) {
		copy_block(buf, (unsigned)stored_len, 0); /* without header */
		compressed_len = stored_len << 3;
	} else if (stored_len+4 <= opt_lenb && buf != (char*)0) {
		/* 4: two words for the lengths */
		/* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
		 * Otherwise we can't have processed more than WSIZE input bytes since
		 * the last block flush, because compression would have been
		 * successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
		 * transform a block into a stored block.
		 */
		send_bits((STORED_BLOCK<<1)+eof, 3);  /* send block type */
		compressed_len = (compressed_len + 3 + 7) & ~7L;
		compressed_len += (stored_len + 4) << 3;

		copy_block(buf, (unsigned)stored_len, 1); /* with header */
	} else if (static_lenb == opt_lenb) {
		send_bits((STATIC_TREES<<1)+eof, 3);
		compress_block((ct_data *)static_ltree, (ct_data *)static_dtree);
		compressed_len += 3 + static_len;
	} else {
		send_bits((DYN_TREES<<1)+eof, 3);
		send_all_trees(l_desc.max_code+1, d_desc.max_code+1, max_blindex+1);
		compress_block((ct_data *)dyn_ltree, (ct_data *)dyn_dtree);
		compressed_len += 3 + opt_len;
	}
	init_block();

	if (eof) {
		bi_windup();
		compressed_len += 7;  /* align on byte boundary */
	}

	return compressed_len >> 3;
}

/* ===========================================================================
 * Save the match info and tally the frequency counts. Return true if
 * the current block must be flushed.
 */
int ct_tally (dist, lc)
	int dist;  /* distance of matched string */
	int lc;    /* match length-MIN_MATCH or unmatched char (if dist==0) */
{
	l_buf[last_lit++] = (uch)lc;
	if (dist == 0) {
		/* lc is the unmatched char */
		dyn_ltree[lc].Freq++;
	} else {
		/* Here, lc is the match length - MIN_MATCH */
		dist--;             /* dist = match distance - 1 */
		dyn_ltree[length_code[lc]+LITERALS+1].Freq++;
		dyn_dtree[d_code(dist)].Freq++;

		d_buf[last_dist++] = (ush)dist;
		flags |= flag_bit;
	}
	flag_bit <<= 1;

	/* Output the flags if they fill a byte: */
	if ((last_lit & 7) == 0) {
		flag_buf[last_flags++] = flags;
		flags = 0, flag_bit = 1;
	}
	/* Try to guess if it is profitable to stop the current block here */
	if ((last_lit & 0xfff) == 0) {
		/* Compute an upper bound for the compressed length */
		ulg out_length = (ulg)last_lit*8L;
		ulg in_length = (ulg)strstart-block_start;
		int dcode;
		for (dcode = 0; dcode < D_CODES; dcode++) {
			out_length += (ulg)dyn_dtree[dcode].Freq*(5L+extra_dbits[dcode]);
		}
		out_length >>= 3;
		if (last_dist < last_lit/2 && out_length < in_length/2) return 1;
	}
	return (last_lit == LIT_BUFSIZE-1 || last_dist == DIST_BUFSIZE);
	/* We avoid equality with LIT_BUFSIZE because of wraparound at 64K
	 * on 16 bit machines and because stored blocks are restricted to
	 * 64K-1 bytes.
	 */
}

/* ===========================================================================
 * Send the block data compressed using the given Huffman trees
 */
local void compress_block(ltree, dtree)
	ct_data *ltree; /* literal tree */
	ct_data *dtree; /* distance tree */
{
	unsigned dist;      /* distance of matched string */
	int lc;             /* match length or unmatched char (if dist == 0) */
	unsigned lx = 0;    /* running index in l_buf */
	unsigned dx = 0;    /* running index in d_buf */
	unsigned fx = 0;    /* running index in flag_buf */
	uch flag = 0;       /* current flags */
	unsigned code;      /* the code to send */
	int extra;          /* number of extra bits to send */

	if (last_lit != 0) do {
		if ((lx & 7) == 0) flag = flag_buf[fx++];
		lc = l_buf[lx++];
		if ((flag & 1) == 0) {
			send_code(lc, ltree); /* send a literal byte */
		} else {
			/* Here, lc is the match length - MIN_MATCH */
			code = length_code[lc];
			send_code(code+LITERALS+1, ltree); /* send the length code */
			extra = extra_lbits[code];
			if (extra != 0) {
				lc -= base_length[code];
				send_bits(lc, extra);        /* send the extra length bits */
			}
			dist = d_buf[dx++];
			/* Here, dist is the match distance - 1 */
			code = d_code(dist);

			send_code(code, dtree);       /* send the distance code */
			extra = extra_dbits[code];
			if (extra != 0) {
				dist -= base_dist[code];
				send_bits(dist, extra);   /* send the extra distance bits */
			}
		} /* literal or match pair ? */
		flag >>= 1;
	} while (lx < last_lit);

	send_code(END_BLOCK, ltree);
}
